Certain industrial gas applications, such as coal gasification combined cycle systems, often require nearly all of the product from a cryogenic air separation plant, e.g. oxygen and nitrogen, to be at an elevated pressure. One way to achieve this is to compress the product streams taken from the air separation plant. However, such product compression is costly and involves the use of additional compression equipment.
A preferred mode of operation to achieve high pressure product production is to operate the columns of the air separation plant at higher pressures, thus producing the products at higher pressures and reducing or even eliminating entirely the need for final product compression. However, operating the columns of a cryogenic air separation plant at elevated pressures imposes an operating burden on the plant because the separation efficiency is a function of the difference in volatilities of the components of the feed air and such volatility differences are reduced as the pressure increases.
Accordingly, it is an object of this invention to provide a method for operating a cryogenic rectification plant at higher than normal pressures while mitigating the separation burden on the system resulting from such high pressure operation.
In addition, the pumping of liquid oxygen to a higher pressure when the system is operated at high pressures generally leads to especially poor recovery of product oxygen. It is therefore another object of this invention to employ pumping of liquid oxygen in order to minimize the cost of oxygen compression while maintaining acceptable oxygen recovery in a high pressure plant.